Known as a photosensitive photographic material in which organic solvents are employed in composing layer coating compositions is a thermally developable photosensitive material called "Dry Silver". This material commonly comprises a support having thereon two functional layers consisting of a photosensitive layer and a protective layer comprising dyes.
Cited as one method to provide a plurality of functional layers on a support is a successive multilayer coating method in which coating and drying of each layer are repeated, and employed are roll coating methods such as reverse roll coating, gravure coating, etc., or a blade coating, wire bar coating, die coating, etc.
There are simultaneous multilayer coating methods in which employing a plurality of coaters, before drying a previously coated layer, the subsequent layer is applied thereon, and a plurality of layers are simultaneously dried, or employing slide coating or curtain coating, simultaneous multilayer coating is carried out through laminating a plurality of coating compositions on the slide surface.
In the successive multilayer coating method, a plurality of passages through a coating and drying process are required. As a result, abrasion results due to contact with holding rolls in the transporting section, or the functional properties are degraded due to the relatively frequent contact with outside air. Further, coating defects are caused due to foreign matter introduced from the outside. Further, because a plurality of thermal drying processes are provided, from the viewpoint of utilization efficiency of energy, productivity is not good.
In the method in which employing a plurality of coaters, before drying a previously coated layer, the subsequent layer is coated, and a plurality of layers are simultaneously dried, coating defects caused by foreign matter introduced from the outside are markedly decreased. However, because so-called wet on wet coating is carried out, coating defects may be caused due to irregularities of the previously coated layer. The wet on wet coating as described herein denotes that a subsequent coating is carried out before the preceding coating has dried.
In the coating method in which a plurality of coating layers are laminated, coating defects caused by foreign matter introduced from the outside can be minimized. However, mixing between layer tends to result due to the flow, diffusion and density differences of each layer. Specifically in a coating composition employing organic solvents, differences in properties of solvents serves to enhance the mixing between layers, making it difficult to properly realize the function of each layer.
Specifically, in thermally developable photosensitive materials, when mixing occurs between the photosensitive layer and the protective layer, the amount and wavelength of light which passes through the photosensitive layer cannot be controlled. As a result, when the predetermined amount of exposure is given, an excessive shortage of exposure may occur and during subsequent thermal development, the photosensitive layer in a semi-melted state may move up to the surface of the protective layer to deteriorate the properties of the photographic material, and further, to stain the heating roll of the development device.